Perception of three-dimensional (3D) objects is robust and stable, despite fragmentary and discontinuous sensory information. This is especially true for vision which is based only on 2D images. The visual system infers the depth of objects form binocular disparity and other, monocular, depth cues, such as motion parallax, perspective, shading, and occlusion. None of these cues is constantly available, and most of them are ambiguous. While disparity selectivity of cortical neurons is well documented, little is known about the processing in primate visual cortex of the monocular depth cues and the mechanisms of cue combination. The stability of perception suggests the existence of cortical depth representations that are cue invariant. The aim of this research is to determine (a) how elementary 3D features are represented in the visual cortex, (b) how different monocular and binocular cues contribute to this representation, and (c) how information from different cues is combined, especially in situations of ambiguity and conflict. The proposed approach is to study, for the same 3D objects and display conditions, (1) depth perception in human and monkey subjects, and (2) the neuronal activity in cortical areas V1, V2, and V4, of the awake, fixating monkey.